The field of the invention relates to engine control systems for motor vehicles and more particularly to high energy ignition control systems for motor vehicles.
An internal combustion engine operates when sparks are applied by spark plugs to a homogenous air and fuel mixture in the combustion chambers of the engine. After application of the spark to the mixture in the combustion chambers, the sparks ignite the mixture, causing the engine to rotate the crank shaft of the engine. The spark energy is generated by an ignition coil and the time that the current is applied to the ignition coil primary is usually referred to as the dwell or on-time of the ignition coil primary.
Ignition systems may be divided into inductive ignition systems and capacitive discharge ignition (CDI) systems. Inductive ignition systems can further be divided into distributor systems and distributor-less (DIS) systems.
In an inductive, distributor-based system, energy is stored in the coil primary inductance and transferred to a coil secondary inductance and then to the spark plugs for each of the cylinders of the engine. At low speeds, the energy stored in the ignition coil is totally discharged to effect the spark. However, at high speeds, residual energy typically remains stored in the ignition coil even after the spark is discharged. Since distributor-based systems only have a single coil, they can only fire the spark plugs every 90 degrees of crankshaft rotation. Thus, with an 8 cylinder engine, 720 degrees is needed to fire all of the cylinders in the engine.
In a DIS system, multiple ignition coils are used to deliver energy to the spark plugs of the cylinders of the engine. This setup may also include using multiple ended coils, for waste spark DIS, of the same coil to deliver energy to different spark plugs. In waste spark DIS systems, a spark is fired once every 360 degrees. In some coil-per-cylinder DIS, no waste spark is used firing the coil/plug once every 720 degrees. Since a spark is not fired as often in DIS systems as in distributor-based systems, all of the energy from the coil is transferred to the spark plugs before the next ignition cycle begins. In other words, with each ignition cycle, there is no energy remaining in the ignition coils and the ignition coil current begins ramping from a value of zero amperes. In addition, since no residual energy storage occurs in DIS systems between cylinder firings, simple fixed ontime dwell control is usually used in such systems.
In CDI systems, a battery voltage is stepped up to over 400 volts and the energy is stored in a capacitor. The capacitor stored energy is charged by the battery voltage to be later discharged in the ignition coil primary to generate a spark from the ignition secondary to the spark plug. A CDI system may use single or multiple ignition coils. Dwell time control is not provided in CDI systems.
Ignition systems can be coupled to various types of devices. For example, traction control devices are often used to control traction of the vehicle and can be connected directly to the ignition coil of the engine or the ignition mag-input. Traction control devices adjust the operation of the engine so that when the vehicle loses traction, the driver can regain control of the vehicle. Although valuable in normal passenger driver applications, traction control devices are forbidden in most high-speed racing applications, since they give an unfair advantage to drivers employing these devices.
A system and method for adjusting the dwell control parameters in an electronic distributor inductive ignition driving a single ignition coil for an internal combustion engine is provided. The ignition coil stores high energy at all engine operating speeds for high horsepower, high compression racing engines while at the same time providing efficient energy storage and performance at lower speeds. Advantageously, the control device is provided as a compact unit and included as part of the existing distributor assembly of the vehicle.
Previous distributor-based, single ignition coil systems are incapable of effectively managing the energy stored in the ignition coil for all speeds of the engine using dwell control. When dwell control was attempted at all, it was made imprecisely and/or was incapable of controlling a high current ignition coil with low inductance and high energy storage and low power dissipation at high power levels under all operating conditions. Consequently, these previous systems could not effectively manage the stored energy or residual energy of the coil at lower speeds and, at the same time, provide the full stored energy needed by the engine at higher speeds. Undesirable consequences often occurred in previous systems, for instance, the burning out the ignition coil at some speeds and the inability to provide the proper energy at other speeds of operation.
In the system and method of the present invention, dwell control parameters are adjusted in an electronic inductive ignition driving an ignition coil in a highly precise manner providing effective energy management of the energy stored in the ignition coil for all operating speeds and conditions of the engine. The dwell control parameters are managed and adjusted based upon such factors as the operating speed range of the engine, the operating mode of the engine, and how well the engine is performing. Energy and residual energy is thereby stored and managed such that efficient low-speed operation is provided while, at the same time, providing full stored energy at operation at higher speeds. Thus, in contrast to previous systems, the present system and method prevents damaging the coil at some operating speeds while at the same time providing surplus energy storage in the coil at other speeds by efficient and precise control of the stored energy and residual energy in the coil for all operating speeds and modes of the engine.
In one approach, the present system and method manages the excess dwell period of the ignition coil primary current The excess dwell control is responsive to engine acceleration at lower speeds and at higher speeds, which can exceed 6000 RPM per second. Advantageously, the present approach provides for greater amounts of excess dwell at lower speeds and lesser amounts of dwell at higher speeds thereby giving the engine the ability to accelerate rapidly.
The excess dwell may also be adjusted based upon the operating mode of the engine. For example, in cranking mode, no excess dwell is provided. In other operating speed ranges, proportional dwell control is used.
In addition, the excess dwell may be adjusted based upon how well the engine is performing. Specifically, a target excess dwell (margin) is selected and the deviation from a target margin is measured by the system. If the deviation is above an acceptable limit, then an increased margin value is selected. Conversely, a reduced target margin value is used when the present margin value has been observed to be more than adequate for a preselected number of operating ignition cycles. In other words, the margin is selected that gives the minimum excess dwell but still allows full energy for the cylinders of the engine.
Other parameters relating to the coil ignition timing may also be adjusted to manage the energy stored in the ignition coil. For example, the instantaneous coil off time is adjusted by detecting the number of missed excess dwell cycles or the number of double excess dwell errors. Other dwell control parameters may also be adjusted as described herein.
Besides the benefits mentioned above, the present system and method provides other advantages. For example, under some circumstances, it is important to be able to slow the speed or revlimit the engine. By providing dwell time control, the engine is efficiently revlimited without wasting stored energy and without storing energy when the engine speed is greater than the user preselected value. The system may also be quickly returned to a non-revlimited mode of operation with full stored energy after only several ignition cycles.
The present system and method allows the detection of traction control device. For example, a traction control device may be connected to the ignition control system and this device may be detected by the present system. This may be accomplished by sensing the voltage at the coil switch terminal and/or the input duty cycle or sensing a change in amplitude of the mag-pick up input signal. The detection of a traction control device causes the present system to enter a studder mode of operation, indicating such a traction device has been detected and is interfering with ignition and traction control device operation. The detection could result in other actions taken such as indication by alternate mode of tach output operation or a fault indicated at power on that has a timeout reset. The detection of traction control devices is particularly advantageous to detect cheaters in high-speed racing applications where the traction control devices are most often forbidden.
The present system is provided in a compact housing that can easily be integrated into the existing distributor housing of a vehicle. In this regard, a small microprocessor and dual IGBT transistors may be used to provide adjustments for the dwell control parameters. These devices may be included on an insulated metal substrate providing efficient thermal energy management. The substrate can easily be mounted within typical ignition distributors.